This invention relates generally to control of motor operations, and more specifically, to methods and apparatus for providing motor control signals.
Electronically controlled variable speed motors (VSMs), including electronically commutated motors (ECMs) and induction motors are generally used in air handling (blowers, fans) applications in HVAC (Heating, Ventilation, Air Conditioning) systems. The controllers (e.g., circuit boards) that are utilized in many of these HVAC systems generally switch 115 VAC (furnace) or 230 VAC (air handler, heat pump) voltages for control of the motors operation. These switched voltages are applied to the taps of induction motors to invoke different speeds of operation for the induction motor. Heating, cooling, and continuous fan modes of operation may all be a different speed (motor tap). Installations with higher or lower static pressure, due to restrictions in the ductwork and filters, may require additional choices.
In systems where VSMs are utilized instead of induction motors, VSM operational selections are typically made with 24 VAC signals that are available in most systems or even with low voltage DC signals developed on the systems control board. To minimize the changes required by an OEM (Original Equipment Manufacturer) to their system controllers when changing from a standard induction motor to a VSM, a way to accommodate the switching and application of the high voltage signals to be compatible with the low voltage signal inputs of the VSM is needed. While active interfaces are known to interface controllers to VSMs, a passive inexpensive solution would also be desirable.